/Engine/Source/Runtime/CoreUObject/Public/Serialization/BulkDataRegistry.h
Report whether the Package had BulkDatas during load that upgrade or otherwise exist in memoryonly and cannot save all its BulkDatas by reference when resaved. This function only returns the correct information until OnEndLoadPackage is called for the given package; after that it can return an arbitrary value.
uint64 GetBulkDataResaveSize ( [FName](API\Runtime\Core\UObject\FName) PackageName )